HIV infection does not affect active case finding of tuberculosis in South African gold miners

Abstract

Rationale: Gold miners in South Africa undergo annual radiological screening for tuberculosis in an occupational health center of a gold mining company, but the optimal screening algorithm is unclear.

Objectives: To evaluate methods for active case detection of tuberculosis.

Methods: A sequential sample of miners attending annual medical examination was screened for tuberculosis using a symptom questionnaire, chest radiograph, and two sputum specimens for microscopy and culture.

Measurements and main results: There were 1,955 miners included in this study; all were male with a median age of 41 years (range, 20-61 yr). Presence of at least one of a trio of symptoms (new or worsening cough, night sweats, or weight loss) had similar sensitivity (29.4%) to either chest radiograph (25.5%) or sputum smear (25.5%). These sensitivities did not differ by HIV status. Presence of one or more elements of the symptom trio and/or new radiological abnormality substantially increased sensitivity to 49.0%. Specificity of the symptom trio was higher in HIV-uninfected (91.8%) than in HIV-infected persons (88.2%; P = 0.018). Specificity of chest radiography and smear were similar (98.7% and 99.0%, respectively) and did not differ by HIV status (both P values > 0.8).

Conclusions: In a population of gold miners who undergo regular radiological screening, the addition of chest radiography to symptom screening substantially improved the sensitivity and positive predictive value. HIV infection did not alter the sensitivity of the screening tool.

Figure 1.

Schematic of the likely impact of an annual active case-finding program of symptom screen and chest radiograph on tuberculosis prevalence and sensitivity of the screening. Prevalent tuberculosis is divided into symptomatic tuberculosis disease, asymptomatic tuberculosis disease with radiographic abnormalities, and asymptomatic tuberculosis disease with no radiographic abnormalities. Assumptions: (1) Tuberculosis prevalence at final year is 2.5% and is 30% symptomatic, 20% asymptomatic with radiographic abnormalities, and 50% asymptomatic with no radiographic abnormalities, as reported in this article. (2) This is assumed to represent an open cohort of miners who are regularly screened for tuberculosis when joining the workforce and then at regular intervals after this. Hence, prevalence of tuberculosis disease that is asymptomatic with no radiographic abnormalities has remained static in the presence of the screening program. (3) The screening program has reduced the prevalence of symptomatic disease and asymptomatic disease with radiographic abnormalities at the same constant rate, producing the same linear trend in declining prevalence. (4) Sensitivity of the screening program is defined as the proportion of disease that is symptomatic plus the proportion of disease that is asymptomatic with radiographic abnormalities (i.e., it is the proportion of all true active disease that can be detected by symptom and radiographic screening). (5) For illustrative purposes, it is assumed that tuberculosis prevalence was 5% before the screening program. CRX = new or changing radiological abnormality; TB = tuberculosis.